L0301P6 - Origin of Cells and Tissues in the Human Body
__TOC__ Embryo Development Oocyte *a.k.a egg, ovum *coated by the zona pellucida **protein oligosaccharide covering the outside of the egg **prevents egg from implanting in the uterine wall *has undergone first meiotic division resulting in one polar body and one to-be egg *unfertilised Fertilisation and Fusion of Pronuclei *meiosis is completed (i.e. second meiotic division occurs) *sperm fertilises the ovum by penetrating the outer layers of the egg *nuclei containing 23 chromosomes from the sperm and egg move towards each other and fuse *results in the formation of the zygote Cleavage of Early Embyros *actually asynchronous *8 cell stage - each cell still has capacity to form a full embryo *16 cells - morula **after compaction cell have become specialised ** the cells known as blastomeres are given particular fates *cavitation occurs at day 4 Early Blastocyst *hollow ball of cells *occurs four and half days prior to implantation *inner cell mass **blue section in Day 4 in the image (above right ) **where all tissues in the body derive from (made of embryonic stem cells) **will become the "baby" *cavity - blastocele *trophoblast - makes extra-embryonic tissue Oct4 *key regulator in pluripotency *transcription factor that maintains cells in the inner cell mass in the undifferentiated state Late Blastocyst *this stage is reached after implantation *blastocyst hatches form the zone pellucida *attaches to the uterine wall at day 6 *bilaminar disk forms **epiblast - only cells that contribute to the body tissues **hypoblast (a.k.a primitive endoderm) - will give rise to extraembryonic membrane Day 8 of Implantation *syncytiotrophoblast grows into the endometrium *secretes human chorionic gonadotropin **hormone that is detected in urine pregnancy tests Day 10 of Implantation *endometrium encloses the embryo *primitive endoderm forms the yolk sac *amniotic cavity forms Gastrulation *generates the 3 primary germ layers: **endoderm **mesoderm **ectoderm *primitive streak forms on bi-laminar disc *cells migrate through the groove and displace the hypoblast cells to form the definitive endoderm *migrating cells also form the mesoderm  Tissue Derivation *ectoderm **skin, neural tissue, some connective tissue *mesoderm **most connective tissue: muscle, skeleton, kidneys, gonads, heart vessels, blood *endoderm **epithelial tissue *organs will have tissue from all three layers Potency Totipotent *can produce an entire organism *can form an embryo if placed in a uterus *e.g. zygote Pluripotent *gives rise to cell derivatives of all three germ layers *will not form embryo but can form all tissue *e.g. embryonic stem cells Multipotent *gives rise to multiple cell types, typically those of the tissue in which the cells reside, but does not normally generate cell types from all germ layers *e.g. haemopoietic (blood) stem cells, Intestinal stem cells Stem Cells *cells capable of dividing and renewing themselves for long periods *are unspecialised and cane give rise to specialised cell types *stem cells and where they are derived from is a highly controversial issue (ethical issue) Types * adult stem cells * embryonic stem cells * induced pluripotent stem cells (iPS) * tumour derived stem cells Adult Stem Cells *multipotent *can be sourced from basically any tissue in the human body including **bone marrow, skeletal muscle, brain, blood *in the human body, normally used to generate and replace cells of their specific types that are lost through normal wear and tear Embryonic Stem Cells *derived from inner cell mass of the early blastocyst *in the embryo it will give rise to the entire body of the organism including: **fat cells, neurons, macrophages, smooth muscle cell, glial cells *when given the correct growth and differentiation factors *pluripotent *very controversial as to where the embryos are sourced from Induced Pluripotent Stem Cells *using skin cells and reverting them back to pluripotent stem cells *allowing the iPS cells to differentiate into the necessary tissue *avoids many ethical issues regarding embryos *currently there is lots of research into this type of cell Use *disease modelling *cell therapy Controversial Issue *Stem Cell Advertising **many very ill people (e.g. Parkinson’s) go overseas for stem cell therapy **overseas countries often do not have the rigorous trials which are essential in Australia **therapies often have either no effect, or severe adverse effects but little benefit